Mesa website says that the 2:90 can be used as a standalone amp. Has me thinking of getting a 2:90 for use as a really basic amp. With just a volume and presence knob and 180 total watts it seems like it would be a pretty pure pedal platform for stereo effects. How is it when used sans preamp?

The 2:90 is the greatest 6L6 platform I've ever had the pleasure to own. MORE amps should just have two knobs just like the 2:90: Volume and Presence. That's all you need! This is actually great for pedals because getting your pedals to play well with any given amp's tone stack (Bass, Mid, Treble) controls is always a pain.